What is GMP?

GMP is a free library for arbitrary precision arithmetic, operating on
signed integers, rational numbers, and floating-point numbers. There is no
practical limit to the precision except the ones implied by the available
memory in the machine GMP runs on. GMP has a rich set of functions, and the
functions have a regular interface.

GMP is carefully designed to be as fast as possible, both for small operands
and for huge operands. The speed is achieved by using fullwords as the basic
arithmetic type, by using fast algorithms, with highly optimised assembly code
for the most common inner loops for a lot of CPUs, and by a general emphasis on
speed.

The first GMP release was made in 1991. It is continually developed and
maintained, with a new release about once a year.

Since version 6, GMP is distributed under the dual licenses,
GNU LGPL v3
and GNU GPL v2.
These licenses make the library free to use, share, and improve, and allow you
to pass on the result. The GNU licenses give freedoms, but also set firm
restrictions on the use with non-free programs.

GMP is carefully developed and maintained, both technically and legally. We
of course inspect and test contributed code carefully, but equally importantly
we make sure we have the legal right to distribute the contributions, meaning
users can safely use GMP. To achieve this, we will ask contributors to sign
paperwork where they allow us to distribute their work.

GMP function categories

There are several categories of functions in GMP:

High-level signed integer arithmetic functions (mpz). There are about 150
arithmetic and logic functions in this category.

High-level rational arithmetic functions (mpq). This category consists of
about 35 functions, but all signed integer arithmetic functions can be used
too, by applying them to the numerator and denominator separately.

High-level floating-point arithmetic functions (mpf). This is the GMP
function category to use if the C type `double' doesn't give enough
precision for an application. There are about 70 functions in this
category. New projects should strongly consider using the much more
complete GMP extension library mpfr
instead of mpf.

C++ class based interface to all of the above. (The C functions and types
can of course be used directly from C++ too.)

Low-level positive-integer, hard-to-use, very low overhead functions are
found in the mpn category. No memory management is performed; the caller
must ensure enough space is available for the results. The set of
functions is not always regular, nor is the calling interface. These
functions accept input arguments in the form of pairs consisting of a
pointer to the least significant word, and an integral size telling how
many limbs (= words) there are in that argument. The functions in the
other categories call mpn for almost all their calculations. Of these
functions about 60 are public.

To try to verify that the file you have downloaded has not been tampered
with, you can check that the GnuPG signature matches the contents of the file.
Use your
GnuPG software or a
key server directly to get the key that was
used for creating the signature. Starting from the repackaging of gmp-5.1.0 as
gmp-5.1.0a.tar.* the following key is used to sign GMP releases:

Instead of using a release, you may also get the latest code from the
GMP repositories. This will require some
more work compared to using a release.

Reporting bugs in GMP

Please first see the
manual on how to report bugs. The
proper address for bug reports is gmp-bugs at gmplib.org.

Most problems with GMP these days are due to problems not in GMP, but with
the compiler used for compiling the GMP sources. This is a major concern to
the GMP project, since an incorrect computation is an incorrect computation,
whether caused by a GMP bug or a compiler bug. We fight this by making the GMP
testsuite have great coverage, so that it should catch every possible
miscompilation.

Note that we perform spam and virus filtering of these lists. The lists
have been 100% spam-free during the last years.

You cannot subscribe an AOL address to any GMP mailing list,
since AOL blocks our mail server until we register with them as a "bulk
mailer", something we will certainly never do.

We're blocking all mail from China, since 99% of the spam
arriving to the GMP moderators emanates from China. If you are affected but
have a legitimate reason to send mail to the GMP project, e.g., if you work at
a university or corporation with an interest in GMP, please let us know; we
will open access for you.

Status of the current release

The current stable release is 6.0.0, released 2014-03-24.

Issues with GMP 6.0.0:

[No issues found yet.]

Issues with GMP 5.1.3:

The documentation of mpn_set_str is incorrect and
incomplete wrt allocation requirements.
Patch.

Issues with GMP 5.1.2:

The functions mpn_sbpi1_div_qr_sec and
mpn_sbpi1_div_r_sec compute incorrect results for some
operands. With uniformly distributed random operands, the error is very
hard to trigger, and for the intended use of these functions, operands can
be expected to appear as such random operands from these functions'
perspective. Patch.

The internal function mpn_divrem_2 on Itanium clobbers two callee-saves
registers. This can lead to miscomputations or crashes in the callers.
Patch.

See also issues for subsequent releases above.

Issues with GMP 5.1.1:

Windows only: A 64-bit build for AMD Bulldozer and Piledriver chips, or
a fat 64-bit build running on these chips, will not work correctly.
Patch.

The function mpz_powm_ui computes garbage if the base
argument is over 15000 decimal or the mod argument is at least 7500 decimal
digits. No other GMP powm function is affected.
Patch.

See also issues for subsequent releases above.

Issues with GMP 5.1.0:

The mini-gmp.c file, which implements a subset of mpn and mpz, was not
properly tested and contained a number of bugs. Please do not use the
5.1.0 version of mini-gmp.c. Note that these bugs do not affect GMP
itself.

The included top-level Makefile.in has an automake-generated
distcheck target which creates a world-writable directory.
This target is not used in the GMP release process, but it is a potential
security problem affecting users who invoke this make target. This
problem (and no other) is corrected in the gmp-5.1.0a.tar.* set of
files.